Plastic hairspring

ABSTRACT

A spiral hairspring is molded from a resilient plastic material so that the several turns thereof are interconnected by a plurality of bridges to facilitate flowing the plastic material throughout the narrow confines of the mold passages. The interconnecting bridges are then cut from between the several turns to form the hairspring. Also, the hairspring may be molded integral with a shaft having a pinion gear thereon.

United States Patent 151 3,696,687 Harland [451 Oct. 10, 1972 [54] PLASTIC HAIRSPRING 2,375,357 5/1945 Friedmon ..267/148 X 72 Inventor: Phili W. Harland P k ,P 1 p er asle a Primary Examiner-Arthur T. McKeon [73] Assignee: Ametek, Inc., New York, NY. Attorney-Smythe & Moore [21] Appl' 127,974 A spiral hairspring is molded from a resilient plastic material so that the several turns thereof are interconnected by a plurality of bridges to facilitate flowing the Plastic material throughout the narrow confines of 58 Id 148 166 the mold passages. The interconnecting bridges are 1 o c l then cut from between the several turns to form the 74/431433 hairspring. Also, the hairspring may be molded integral with a shaft having a pinion gear thereon. [56] References Cited 8 Claims, 4 Drawing Figures UNITED STATES PATENTS 680,234 8/1901 Eaton et a1. ..74/432 PATENTEDnm 10 L912 INVENTOR W A A L mvp ATTORN EYS PLASTIC IIAIRSPRING Spiral hairsprings constructed of high grade spring metals have been used in various types of gauges, measuring instruments, and similar devices. One end of the hairspring is attached to a shaft which extends outwardly of the gauge and on the end of which is mounted an indicator pointer. The shaft is provided with a pinion which may be engaged by a sector or other gear actuated by an instrument movement in response to conditions sensed by the instrument. The outer end of the hairspring is generally fixed to a stationary post. The inner end is generally affixed to the pinion shaft by staking or some other suitable process. In view of the relatively small sizes of these components, the attaching of the hairspring to the shaft tends to complicate the assembly process.

One of the objects of the present invention is to provide an improved spiral hairspring molded from synthetic plastic material.

Another object of the present invention is to provide a spiral hairspring molded integrally with a pinion gear.

Another object of the invention is to provide a spiral hairspring molded from plastic in such a manner that a uniform flow of plastic throughout the long spiral path of the spring is readily achieved.

According to one aspect of the present invention, a spiral hairspring is molded from resilient plastic material by gating the narrow confines of the mold passages utilizing one or more bridges crossing the spiral cavity and interconnecting with adjacent turns to provide an increased passage for the flow of plastic material. The molded hairspring would then have one or more bridges interconnecting the turns thereof. After the hairspring is molded, the bridges between the turns are removed by cutting to form the spiral hairspring. The spiral hairspring may be molded integrally with a pinion gear or with a shaft upon which a pinion is integrally formed.

Other objects, advantages and features of the invention will become apparent from the following description and drawings, which are merely exemplary.

In the drawings:

FIG. 1 is a vertical sectional view of a gauge incorporating the spiral hairspring according to the present invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1 showing the spiral hairspring;

FIG. 3 is a top plan view of the hairspring as it is taken from its mold and showing the radial bridges interconnecting the turns thereof; and

FIG. 4 is a sectional view taken along the line 44 of FIG. 3 and showing the manner in which the bridges can be cut between the turns of the hairspring.

Proceeding next to the drawings wherein like reference symbols indicate the same parts throughout the various views, a specific embodiment of the present invention will be described in detail.

A gauge indicated generally at in FIG. 1 is provided with a hairspring 11 whose inner end 12 is affixed to a pinion shaft 13 and whose outer end 14 is attached to a pin 15 (FIG. 2) within the instrument. Shaft 13 is provided with a pinion gear 16 in mesh with a sector gear 17 carried by a pivotally mounted shaft 18. The

sector gear is a component of an instrument movement which is actuated in response to the particular condition being sensed by this gauge.

The shaft 13 extends outwardly of movement plate 19 and has an indicator pointer 20 attached to its outer end. The pointer cooperates with the usual dial.

Hairspring 11 is in the shape of a spiral as may be seen in FIG. 2 and comprises a plurality of turns. The hairspring is molded from a resilient plastic material, such as acetal or nylon. The pinion shaft 13 and pinion gear 16 may be integral with the hairspring.

In the molding of the hairspring, a mold having a spiral cavity is used to form the several turns of the hairspring in the shape as shown in FIG. 3. The mold cavity also may contain the necessary configuration to form the shaft 13, or the gear 16 or both. The mold may be gated at any convenient point. Thus, in its fluid or molten form, the hairspring is integral with the shaft 13 and its inner end 12 is connected to the shaft in the manner shown in FIG. 2.

The mold can also be provided with one or more bridges 21 which may be radial and which may extend outwardly from the shaft 13. The bridges also could be chords or located other than in a radial configuration. These bridges extend from the shaft to the outermost turn, as may be seen in FIG. 3, and interconnect with the intermediate turns of the hairspring. As a result, the plastic introduced into the mold will flow throughout the entire path of the mold cavity including the narrow confines of the spiral cavity by means of the bridges. While only two radial bridges have been shown in FIG. 3, it is understood that one or more than two may be employed if so desired, and bridges other than radial bridges may be employed. The bridges may be equally spaced to ensure a uniform distribution of the molten plastic throughout the mold cavity.

Merely by way of example, upon removal of the molded unit comprising the hairspring, shaft and pinion, the molded unit may be placed in a fixture, as shown in FIG. 4, having a tubular extension 22 which receives the shaft 13 and a plurality of knife edges or blades 23 for the purpose of severing the bridges 21 between all of the turns of the hairspring. Upon cutting the bridges, the spring will be as shown in FIG. 2.

Preferably, one of the bridges 21A across the turns of the hairspring is located adjacent the outer end of the spring so as to trap or engage the flexible or resilient turns so the assembly of hairsprings, pointer and shaft will not tangle when the parts are handled or are automatically fed from a hopper to an assembly machine. After the parts have been automatically or otherwise positioned, the bridges can be cut because then there is no more problem existent because of parts tangling. Even if multiple gating is used so that bridges are not needed, it is necessary or desirable to tie in the outer coil loose end and then to cut the same after the parts are positioned.

The completed hairspring may be heat treated so as to be hardened as is known in plastic technology. Use of such a plastic hairspring assembly in a gauge gave accurate results which are closely comparable to the results achieved by the conventional metal hairspring.

In addition to nylon, it has been found that Celcon," a trademark of Celanese Corporation for its brand of acetal, a copolymer of trioxane, works satisfactorily. One form has a tensile strength yield p.s.i. of 8,800, elongation percent, flexural strength p.s.i. 13,000, and work energy (in lb./in. of 730.

Delrin, a trademark of E. l. DuPont de Nemours &'

Co. for its brand of an acetal resin.

Thus, it can be seen that the present invention has disclosed a novel form of plastic hairspring which may be formed integral with a shaft and pinion and which has uniform properties throughout since the use of bridges facilitates the uniform distribution of the plastic throughout the mold cavity as it is being fed thereto.

It will be understood that various details of construction and arrangement of parts may be made without departing from the spirit of the invention except as defined in the appended claims.

What is claimed is:

1. As an article of manufacture, a spiral hairspring of resilient synthetic plastic material and molded integrally with a pinion gear.

2. An article of manufacture as claimed in claim 1 wherein a shaft for the pinion gear is molded integrally therewith.

3. An article of manufacture as claimed in claim 1 wherein the pinion gear is integral with a shaft and an end of the hairspring is integral with the shaft and pinion gear to define a unitary pinion gear, shaft and hairspring. p

4. An article of manufacture as claimed in claim 1 wherein said hairspring has a plurality of turns.

5. An article of manufacture as claimed in claim 2 wherein the unitary hairspring, pinion gear and shaft are molded of acetal resin.

6. An article of manufacture as claimed in claim 2 wherein the unitary hairspring and gear are molded of nylon.

7. An article of manufacture as claimed in claim 1 wherein there is a means provided to tie in the outer end of the hairspring to the adjacent inner coil so as to facilitate assembly without tangling.

8. An article of manufacture as claimed in claim 7 wherein the means to tie in the outerend of the hairspring will hold the assembly so that it can be fed from a hopper to an assembly machine. 

1. As an article of manufacture, a spiral hairspring of resilient synthetic plastic material and molded integrally with a pinion gear.
 2. An article of manufacture as claimed in claim 1 wherein a shaft for the pinion gear is molded integrally therewith.
 3. An article of manufacture as claimed in claim 1 wherein the pinion gear is integral with a shaft and an end of the hairspring is integral with the shaft and pinion gear to define a unitary pinion gear, shaft and hairspring.
 4. An article of manufacture as claimed in claim 1 wherein said hairspring has a plurality of turns.
 5. An article of manufacture as claimed in claim 2 wherein the unitary hairspring, pinion gear and shaft are molded of acetal resin.
 6. An article of manufacture as claimed in claim 2 wherein the unitary hairspring and gear are molded of nylon.
 7. An article of manufacture as claimed in claim 1 wherein there is a means provided to tie in the outer end of the hairspring to the adjacent inner coil so as to facilitate assembly without tangling.
 8. An article of manufacture as claimed in claim 7 wherein the means to tie in the outer end of the hairspring will hold the assembly so that it can be fed from a hopper to an assembly machine. 